The approval of tissue plasminogen activator (tPA) for use in acute ischemic stroke by the FDA in 1996 dramatically changed the treatment of stroke. Yet, many patients who are potential candidates do not receive thrombolytics due to the treating physician's concern of hemorrhage. New diagnostic tests to identify patients at increased risk of tPA-associated hemorrhage, to predict long-term outcome, and to measure therapeutic efficacy would ve very useful to physicians who treat acute stroke patients with tPA or other therapies. This proposal will examine the relationship of serum proteins to baseline stroke severity, clinical and radiographic outcome, response to therapy, and the risk of intracerebral hemorrhage after tPA+/- eptifibatide therapy in the CLEAR Trial. In Aim 1, based on our preliminary findings, two serum proteins, S100 and myelin basic protein (MBP), will be studied over the first 24 hours from presentation. Changes and peaks in S100 and MBP concentrations will be correlated with the severity of neurologic deficit, volume of infarct on CT and magnetic resonance imaging, flow in the middle cerebral artery as measured by magnetic resonance angiography, presence of intracerebral hemorrhage, and long-term outcome. Aim 2 will employ a proteomics approach to identify plasma proteins that are associated with intracerebral hemorrhage following administration of tPA. Pretreatment plasma from patients who do not develop intracerebral hemorrhage. A long-term goal of this study is to develop serum marker assays as independent measures of prognosis and therapeutic efficacy. Such tools would be useful in the design of new clinical therapeutic trials and the selection of therapies in acute stroke. Long-term goals associated with the proteomics study include developing rapid assays that could be used to identify patients at increased risk of hemorrhage to better select patients for thrombolytic therapy. Additionally, the protein library created by this project could help identify new proteins associated with ischemic stroke leading to improved diagnostic assays with increased sensitivity, specificity, and accuracy for cerebral ischemia. Overall, this project in conjunction with Project 3, represents a unique opportunity to compare both a proteomics and genomics approach in a single disease condition, thereby complementing each strategy's strengths. We expect this project will lead to the development of further proteomics and genomics studies of ischemic and hemorrhagic stroke.